Bipedialism And Humans

Walk Like a Man

The Causes and Effects of Bipedalism

Very few of us appreciate our history of becoming bipeds, mostly because walking requires so little energy and little thought. Many people think that our high intellect or the ability to grasp items with our opposing thumbs is what sets us apart from other primates. All primates share the grasping thumb, and the difference between a human brain and an ape brain is not as great as people perceive it to be. The human brain is basically a bigger and more complicated version of a chimpanzee brain. The main difference between humans and primates are that humans can walk on two legs. Although Homo sapiens aren't the only primates to walk on two feet, no other primate does it so often. Many evolutionary biologists and anthropologists have come up with many reasons as to why hominids started to walk upright.

There are many different explanations as to why hominids started to walk upright. One of the main hypothesized causes of bipedalism is that walking on two legs is a more energy efficient way of moving around than a quadruped. When hominids first had to adapt to an open environment the ones that could walk on two feet would be able to search for food longer. Another reason why bipedalism came about is that the hands would not have to help the hominid walk and hominids would be able to make tools and gather food more efficiently. Anthropologists and biologists now agree that upright posture and walking on two legs was the crucial and probably first major adaptation associated with the divergence of the human lineage from a common ancestor with the African apes.

Standing on two feet is an extremely odd posture and an even more odd way to walk. There are more than two hundred species of primates on earth today and only one of them is bipedal. Although other primates are able to walk on two feet for short periods of time, we are the only ones that can maintain that posture for long periods of time. If you take all the species of mammals, there are very few that can walk and stand bipedally. Almost all other mammals stand and walk or run on four limbs. Those that stand on two feet have quite different postures and gaits from humans. If you include the other types of animals, such as reptiles, walking on two feet as opposed to four is the rarest way to get around. Our entire body, from the spine and pelvis and even all the way to the nervous and circulatory systems, has changed because of bipedalism.

As opposed to most arboreal quadrupeds that stay high up in trees, most hominids that walk on two legs spend time on the ground. The pounding on the feet took its toll with more time being spent on the ground and also traveling at faster speeds. In the foot anatomy, when comparing current humans with the early hominids, there is a major difference between the ways in which weight is transmitted along the hominids and human feet. In early hominid movement, the weight is mostly along the side of the foot and the push off is through the middle of the toes. In a human, the body weight is passed along the outside of the foot and the push off is made by the big toe. The human style is much more efficient for striding (Hunt 1993: 189-193). The toes might have been aligned this way because of the tendency of the hominids to stand up and monitor the surroundings. This would help to develop feet that can withstand the entire body weight. The change in the foot structure enabled an upright stance. These changes could have occurred rapidly and the primary reason for switching to a bipedal stance might have been because of conserving energy.

There are differences in the knee joint of modern humans, early hominids and chimpanzees. The knee of a hominid and modern human resembles each other in having the typical carrying angle of bipeds. In the chimpanzee, the thigh and shin bones form a straight line, this posture is ideal for walking on all four legs. In humans and early hominids, the thigh and shin bone from an angle, so that the thighs come together at the knees which enables us to walk in a straight line (Berge 1993: 260-266). The pelvis has also gone through drastic changes. The pelvis in the australopithecine shows that the pelvis in these hominids is rounded and shallow and the femurs are tilted toward the midline. This shows that the body weight is being transmitted directly downward to the knees. Also the width of the pelvis is larger in humans than early hominids, which is the result of not only more efficient walking, but also it enabled modern humans to give birth to infants with larger skulls. All of these anatomical changes help allow the proper maintaining of balance and enables us to walk on two legs (Hunt 1993: 194-196). Bipedalism changed the bone structure of the hip, foot and even the pelvis and there are many biologists, like Charles Darwin, who have come up with reasons for why early hominids started to walk on two legs.

When evolution is discussed, the first person that comes to mind is Charles Darwin. He was the first person, after Aristotle, to write about bipedalism. Darwin developed the oldest theory of bipedalism. He believed that bipedalism came about in order to free the hands so that humans could use their hands to carry items, such as food and weapons. In 1871 Darwin wrote, "If it be an advantage to man to stand firmly on his feet and to have his hands and arms free . . . then I can see no reason why it should not have been advantageous to progenitors of man to have become more erect or bipedal" (Standford 2003: 8). He felt that since most hominids were hunting animals, bipeds would be better suited to hunt and use weapons. Now that the hands wouldn't be used in walking, hominids could use their hands to use more effective hunting techniques, like throwing rocks and arrows. Since quadrupeds use their hands to walk they would be at an extreme disadvantage when it comes to hunting. They could not rely on their hands to throw weapons and gather their prey. He also proposed that bipedalism came after large brains evolved (Standford 2003: 9).

Today it is known that more complex brains appeared after bipedalism came about. Darwin had little knowledge of the fossil records when he recorded his findings. Darwin also came up with the idea that mothers or fathers had to carry their infant babies. He said that people walking on two feet would be able to carry meat home from animals that they have killed because they have free hands (Standford 2003: 9).

One problem with the two aforementioned causes is that even though chimpanzees are not habitual bipeds, they can still carry their young and meat; bipeds are just must more efficient. Darwin's theory of bipedalism is largely discredited now, as a means